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Final Report: Development of All-Solid-State Sensors for Measurement of Nitric Oxide and Carbon Monoxide Concentrations by Optical Absorption

EPA Grant Number: R828180
Title: Development of All-Solid-State Sensors for Measurement of Nitric Oxide and Carbon Monoxide Concentrations by Optical Absorption
Investigators: Walther, Thomas , Caton, Jerry , Lucht, Robert P.
Institution: Texas A & M University
EPA Project Officer: Shapiro, Paul
Project Period: July 1, 2000 through June 30, 2002
Project Amount: $225,000
RFA: Exploratory Research - Physics (1999)
Research Category: Engineering and Environmental Chemistry

Description:

Objective:

The overall objective of this research project was to develop new optical sensors for the detection of nitric oxide (NO) and carbon monoxide (CO) in the exhaust streams of combustion systems. Sensors based on absorption measurements combine high sensitivity and real-time capabilities. Present sensors rely on physical sampling techniques that are inherently slow.

The specific objectives of this research project were to: (1) develop a diode-laser-based UV absorption sensor for NO measurements and a diode-laser-based mid-infrared absorption sensor for CO measurements; (2) characterize the performance of the sensors by absorption measurements in a gas cell, simulated combustion exhaust streams, and well-characterized flames, and by comparison with Fourier Transform Infrared Spectroscopy (FTIR) measurements and/or probe sampling; and (3) complete a feasibility study of the incorporation of the sensor systems in practical systems for pollutant monitoring and control.

Summary/Accomplishments (Outputs/Outcomes):

The objectives of the research project have been accomplished. We have successfully developed both the NO sensor and the CO sensor, and tested these sensors in gas cells filled with calibrated gas mixtures. The sensor concentration measurements were in good agreement with the calibrated gas mixture concentrations. In lieu of a feasibility study of the incorporation of these sensor systems in practical systems, we used the sensors to perform measurements in the exhaust of an operating gas turbine engine at Honeywell Corporation in Phoenix, AZ, and in a particle-laden exhaust flow from a coal combustor.

An all-solid-state continuous-wave (cw) laser system for ultraviolet absorption measurements of the NO molecule was developed and demonstrated. The single-mode, tunable output of a 10-mW, 395-nm external-cavity diode laser (ECDL) is sum-frequency-mixed with the output of a 115-mW, frequency-doubled, diode-pumped cw Nd:YAG laser in a beta-barium borate crystal to produce approximately 50 nW of tunable cw radiation at 226.7 nm. The wavelength of the 395-nm ECDL is then scanned so that the wavelength of the ultraviolet beam is tuned over NO absorption lines to produce a fully resolved absorption spectrum. Ultraviolet laser radiation is detected using a solar-blind photomultiplier tube. The estimated NO detection limit of the system for a demonstrated absorption sensitivity of 2x10-3 is 0.2 ppm per meter of path length for 300 K gas. Measurements were performed in a gas cell using calibrated mixture of NO in N2 buffer gas, and the concentrations obtained from the absorption measurements are in good agreement with the calibrated concentrations.

The diode-laser-based CO sensor layout is based on difference-frequency-mixing in a periodically poled lithium niobate crystal to obtain approximately 1 µW of narrowband, cw laser radiation at 4.5 mm. The fundamental beams for this nonlinear process are 1,064 nm and 861 nm. The 1,064-nm laser is a Nd:YAG system that provides 550 mW of 1,064.664 nm radiation. The 861-nm laser is an 80-mW tunable ECDL system that can be tuned mode-hop free over a 10 GHz range. The ECDL radiation is tuned so that the generated Infrared (IR) is tuned over the R-branch transitions of the CO molecule. Once the mid-infrared laser radiation is generated, the beam is split into a reference beam, a second beam that is sent through the gas cell or through exhaust gases. Both beams are detected using Indium Antimonide (InSb) detectors.

Both of these sensors were used for measurements in the exhaust stream of an operating auxiliary power unit gas turbine engine in a series of tests at Honeywell in Phoenix, AZ, during July. During these tests, NO was measured in the exhaust at levels below 10 ppm. For measurements at levels above 20 ppm, the NO emission levels obtained using our new ultraviolet absorption sensor agreed with the results of probe sampling chemiluminescent analyzer results to within 1-2 ppm. The results of the CO mid-IR absorption measurements are being analyzed, but concentrations obtained from our absorption measurements appear to be approximately a factor of two (low compared to probe sampling measurements). We currently are investigating our CO spectral model and potential CO2 interferences in gas cell measurements in an attempt to understand the source of this discrepancy.


Journal Articles on this Report: 2 Displayed | Download in RIS Format

Other project views: All 13 publications 2 publications in selected types All 2 journal articles

Type Citation Project Document Sources
Journal Article Hanna SF, Barron-Jimenez R, Anderson TN, Lucht RP, Caton JA, Walther T. Diode-laser-based ultraviolet absorption sensor for nitric oxide. Applied Physics B-Lasers and Optics 2002;75(1):113-117. R828180 (2002)
R828180 (Final)
 not available
Journal Article Ray GJ, Anderson TN, Caton JA, Lucht RP, Walther T. OH sensor based on ultraviolet, continuous-wave absorption spectroscopy utilizing a frequency-quadrupled, fiber-amplified external-cavity diode laser. Optics Letters 2001;26(23):1870-1872. R828180 (2000)
R828180 (2002)
R828180 (Final)
 not available
Supplemental Keywords:

pollutant monitor, pollutant emissions, diode lasers, optical sensors, nitric oxide, carbon monoxide, fiber amplifiers. , Toxics, Air, Scientific Discipline, Waste, RFA, Engineering, Chemistry, & Physics, EPCRA, HAPS, Physics, Incineration/Combustion, Environmental Chemistry, Environmental Monitoring, tropospheric ozone, risk assessment, ambient emissions, nitrous oxide, chemical detection techniques, diode laser, fiber ampiliers, combustion systems, air sampling, diode laser spectrometer, nitric oxide (NO), carbon monoxide, combustion, Nitric oxide, Fourier Transform Infrared measurement, measurement methods , carbon monoxide (CO), air quality standards, laser based optical sensor, optical absorption, pollutant monitoring, probe sampling
Relevant Websites:

http://faculty.physics.tamu.edu/walther exit EPA
http://tools.ecn.purdue.edu/~lucht/ exit EPA

Progress and Final Reports:
2000 Progress Report
2002 Progress Report
Original Abstract

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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